In the production of edible oils and fats the oil is refined and the neutralized and bleached oil is subsequently supplied to a deodorizing stage in which the undesired flavoring and factory substances are removed. These substances consist mainly of alcohols, ketones, aldehydes and low-molecular weight fatty acids and, more recently, also of traces of chlorine-containing pesticides.
The impurities are usually steam distilled at elevated temperature and under reduced pressure in a closed apparatus. Such a process has been described in Chemikerzeitung 88, pages 412 et seq.
The process can be carried out as a batch process, a semicontinuous process or a continuous process (Fette, Seifen, Anstrichmittel 72, pages 166 et seq., 1970).
It has been attempted to improve the semicontinuous process by continuously feeding the product to the first stage of the plant and continuously discharging the product from the last stage whereas the intervening stages are intermittently operated in alternation. This practice allows direct heat exchange in a separate heat exchanger between the hot product as it is discharged and the cold product as it is fed. Such a procedure has the disadvantage that owing to the continuous feeding and discharge the treating time of the oil in the first and last stages is not uniform. Here too, portions of the oil are treated for a longer of shorter time. A restriction is also involved in the requirement that one and the same product must be processed for long periods of time and there is no frequent change of product. It is also known to design the first stage as a heat exchanger and to heat this stage by a closed heat carrier cycle. In the practice the cooled heat carrier is reheated by the heated product in one of the subsequent stages.